1. Field of the Invention
The present invention relates to a liquid crystal display element and a method for manufacturing the same, and more particularly to a method of dispersing spacers and liquid crystal display elements made by the method, capable of lengthening the life of twisted nematic (TN) and super twisted nematic (STN) which require high reliability.
2. Description of the Prior Art
Referring to FIG. 1 there is shown an example of general liquid crystal display elements. As shown in the drawing, the liquid crystal display element comprises upper and lower glass substrates 1 and 1', each coated with an ITO (Indium Tin Oxide) film which is a transparent conductive film. On upper and lower glass substrates 1 and 1', photosensitive resin layers are coated. The coating of photosensitive conductive resin layers is carried out under the condition that upper and lower glass substrates 1 and 1' have been cleaned and then dried to remove moisture therefrom. As the photosensitive resin layers are selectively radiated with light, transparent conductive films coated on upper and lower glass substrates 1 and 1' are etched to form an upper common electrode 3 and a lower pixel electrode 3' having desired patterns, respectively. That is, upper and lower transparent conductive films are patterned to have a 90.degree. crossed matrix shape.
Thereafter, an insulating solution which contains a main solvent of SiO.sub.2 is applied to glass substrates 1 and 1' having patterned transparent conductive films by using a coating method. The insulation solution is then dried to volatilize its solvent, thereby forming insulation layers 4 and 4', each having a thickness of about 500 .ANG., on the glass substrates 1 and 1'.
On insulation layers 4 and 4', polyimide layers are coated to form oriented layers 5 and 5', by using a roll coating method. Between oriented layers 5 and 5', spacers 7 are interposed. The interposition of spacers 7 can be accomplished by coating polyimide layers in which spacers are mixed, or dispersing spacers after coating polyimide layers. In the latter case, the coated poyimide layers are subjected to scratching and rubbing.
Subsequently, a seal 8 is formed by a screen printing. Then, upper and lower glass substrates 1 and 1' adhere to each other by using a pressure setting, so as to form a plurality of liquid crystal cells between oriented layers 5 and 5'. The obtained structure is then cut by being subjected to a mechanical impact, for example, by using a silicon carbide or diamond cutter so that it is divided into respective liquid crystal cells.
In order to inject a liquid crystal into respective liquid crystal cells, liquid crystal cells together with a container containing liquid crystal therein are then disposed in a vacuum chamber. The container is subjected to ultrasonic wave to extract moisture and air bubbles from liquid crystal, under the condition of letting air out of the vacuum chamber. After the chamber is at a vacuum state, nitrogen gas is injected into the chamber under the condition that the liquid crystal is in contact with an inlet of each liquid crystal cell. As the nitrogen gas is injected into the chamber, the liquid crystal enters the liquid crystal cells, by virtue of the difference between the pressure in each liquid crystal cell and the pressure in the chamber and a capillary phenomenon. After the completion of injecting liquid crystal into cells, the inlet of each cell is sealed by a photosetting resin, to prevent the liquid crystal 6 in the cell from contacting air and moisture contained in the air.
Finger marks and organic matters on liquid crystal cells are then removed. Subsequently, polarizing plates 2 and 2' are adhered to outer surfaces of upper and lower glass substrates 1 and 1', respectively. In order to obtain a good adhesion, liquid crystal cells are cleaned by a freon gas for about 20 seconds, before the adhesion.
Typically, the above-mentioned dispersion of spacers 7 in manufacturing liquid cells is accomplished by using either of the following two methods.
One is method which comprises the steps of mixing spacers in an oriented layer producing solution at a proper mixing rate, coating the produced mixture on insulation layers to form oriented layers containing spacers interposed therebetween, and then setting the formed oriented layers.
The other is a method which comprises the steps of coating the oriented layer producing solution alone on insulation layers, rubbing the produced oriented layers, and dispersing spacers of being mixed with air or volatile liquid, between oriented layers, before the adhesion of upper and lower glass substrates.
The position of spacers varies depending on the used dispersing method. For example, the position of the spacer 7 shown in FIG. 1 corresponds to the first method, while the position of the spacer 7' the second method.
The first method is mainly used in the case where the oriented layers are of an organic high-molecular material containing polyimide as its main ingredient and the spacers are of a mineral material containing lass fiber or aluminum oxide (Al.sub.2 O.sub.3). In case of dispersing spacers under the condition of being mixed in the oriented layer producing solution, by using the first method, pin holes may occur in the formed oriented layers, due to the surface tension generated between each spacer and the solution and the difference between the cohesion of each spacer and the cohesion of the solution. Furthermore, the formed oriented layers may have irregular thickness due to the same causes. Upon rubbing, the spacers may be displaced from their original positions, thereby causing the oriented layers to be damaged. In case when the spacers are broken, there may be a disadvantage that the gap in liquid crystal cell can not be uniformly maintained.
In the second method wherein spacers are dispersed after rubbing of oriented layers, surfaces of upper and lower glass substrates are subjected to a vacuum cleaning, in order to remove dirts or contaminants therefrom, before upper and lower glass substrates adhered to each other. Since the vacuum cleaning is carried out after rubbing of oriented layers, foreign matters may enter the gap, thereby causing the gap to be poor.